GafChromic MD-55 Film Research Articles

Assessment of image-guided CyberKnife@ radiosurgery for metastatic spine tumors

Spinal metastases are associated with significant symptoms. From September 2005 to September 2007, 69 consecutive patients with 127 malignant spine metastatic lesions were treated at Wanfang Hospital with CyberKnife (CK) radiosurgery. The radiosurgery dose ranged from 10 to 30 Gy (mean 15.5 Gy) prescribed to the 75-85% isodose line that encompassed at least 95% of the tumor volume. We used fiducials as tracking landmarks for CK treatment of the thoracic and lumbar spine. A torso anthropomorphic phantom and GafChromic MD-55 films were used to verify the accuracy of CK radiosurgery and 2D dose distribution, demonstrated high targeting accuracy with 2% average deviation of the measured dose from the estimated dose at the set-up center and less than 5% dose deviation in 2D isodose curve. Visual Analogue Scale and Oswestry Disability Index questionnaires were used to monitor functional outcome after radiosurgery. Local tumor control at 10 months was 96.8%. Mean pain scores decreased significantly from 65 to 30 after treatment (P = 0.001). Functional disability was significantly improved after treatment (P = 0.002). The most common treatment toxicities were nausea and fatigue. In conclusion, CK radiosurgery is a well-tolerated and effective treatment for spine tumors with good local tumor control and a favorable outcome on pain and functional improvement after treatment.

Comparison of 50 kV Facilities for Contact Radiotherapy

The radiation characteristics of a short source to surface distance (SSD) contact therapy tube in clinical use at the Centre Antoine-Lacassagne, Nice and a long SSD unit at the Clatterbridge Centre for Oncology were compared. The output from the tube at Nice had a dose rate of approximately double that of the tube at Clatterbridge, whereas the tube at Clatterbridge had a slightly higher value of the half value layer. Depth dose measurements were made with GafChromic MD55 film and SSD corrected depth dose curves showed good agreement between centres. Profiles at 2mm depth also showed comparable levels of flatness and uniformity.

Estimation of radiation dose at various depths for commonly used radionuclides in radiosynoviorthesis in a tissue equivalent material

The purpose of the paper is to report on the dose estimation studies at various depths for the commonly used beta-emitting 90Y, 166Ho, 153Sm, 32p, and 177Lu radionuclides in a phantom fabricated using the poly methyl methacrylate tissue equivalent material having a density of 1.19 gm/cc, by using thermoluminescent dosemeters. GAFChromic MD-55 films were used to calculate the calibration factor for the thermoluminescent micro-rods used in our study. It is observed that 90Y delivers the highest dose at 1 mm amongst the radionuclides tested followed by 32p, 166Ho, 153Sm, and 177Lu, whereas the cumulative dose received by the joint was found to be more for 32P followed by 90Y, 166Ho, 153Sm, and 177Lu. The highest therapeutic range obtained is 3.1 mm for 153Sm amongst the tested radionuclides. The dose values obtained for all the above-mentioned radionuclides can serve as reference material for those researchers and clinicians who are interested in selection of the radionuclide for the type of joint treated and the amount of dose necessary to be delivered to the synovial membrane.

Dosimetric evaluation of GAFCHROMIC® XR type T and XR type R films

The high spatial resolution of radiochromic film makes it ideal for dosimetric measurements and dose distributions in regions of high dose gradient. Intensity‐modulated radiation therapy, intravascular brachytherapy, and eye‐plaque radiation therapy demand precise spatial dosimetric calculations. Such precision is not possible with conventional dosimeters, such as thermoluminescent dosimeters and ionization chambers. Recently, new GAFCHROMIC® XR type T and type R films have been developed for radiation dosimetry, specifically in interventional radiology procedures. Dosimetric characteristics (i.e., linearity, post‐exposure density growth, energy dependence, dose‐rate dependence, and UV light sensitivity) of these new films were investigated. To evaluate the clinical applications of these films, their characteristics were compared with other commercially available film models. GAFCHROMIC® XR type T and type R films were found to be more sensitive to low‐energy doses as compared with GAFCHROMIC® MD‐55 films.PACS numbers: 87.66‐a, 87.53‐j

Dose evaluation and measurement of the 188Re liquid-filled balloon in intravascular brachytherapy

We compared the Monte Carlo evaluation and GafChromic MD-55 film experimental measurement of 188Re liquid-filled balloons in intravascular brachytherapy using two phantoms of 6 mm vascular diameter, a phantom of 4 mm vascular diameter and a phantom of 3 mm vascular diameter. A dose-evaluation interface program was developed and was shown to be capable of quickly providing information such as the necessary 188Re source irradiation time to deliver a prescribed dose.

Evaluation of dose distribution by using gafchromic MD-55 film in radiotherapy of laryngeal cancer

Evaluation of dose distribution by using gafchromic MD-55 film in radiotherapy of laryngeal cancer

Calculated dose response of Gafchromic MD55 film for 103Pd and 125I relative to 60Co

Generalized cavity theory is used to calculate the dose–response of the radiochromic dye film MD55 to the X- and γ-radiations from 103Pd and 125I. The analysis indicates that for film calibrated using 60Co, the correction factor giving the dose to water is 1.81±0.05 for 103Pd and 1.71±0.05 for 125I.

Optical density changes of Gafchromic MD-55 film resulting from laser light exposure at wavelengths of 671 nm and 633 nm.

Laser-based scanners provide a sensitive means for measuring optical density (OD) of Gafchromic films. Such instruments were reviewed in a recent AAPM report (task group 55) which provided recommendations and information on OD measurements (effect of wavelength, temperature, etc.). The present article reports that variable rate scanners and spot densitometers using laser diodes (671 nm) and HeNe lasers (633 nm) can cause polymerization of Gafchromic film. The light induced polymerization depends on light power, wavelength, beam spot size, dwell time, and prior radiation dose of the film. Measurements were made with a custom built scanner that provided accurate control of light power, light polarization, dwell time, and film position in relation to the beam focus. The results demonstrate that lasers operating with powers of 0.1, 0.5, 1.0, and 1.5 mW produce a nonlinear increase in OD of Gafchromic film. The measured change in OD after 1 min of exposure ranges from 0.150 to 0.244 for a laser diode operating at 0.5 and 1.5 mW, respectively. Tables are included that tabulate the increase in OD for laser power, dwell time, and prior dose. Laser light induced polymerization can have a significant impact on dosimetry measurements acquired using these laser-based systems.

An application of GafChromic MD-55 film for 67.5 MeV clinical proton beam dosimetry

The purpose of this study is to explore the use of GafChromic MD-55 (RC) film for 67.5 MeV clinical proton beam dosimetry at the Crocker Nuclear Laboratory, University of California, Davis. Several strips of RC film 6 cm × 6 cm in dimension were irradiated at a depth of 18.2 mm corresponding to the middle of a 24 mm spread-out Bragg peak (SOBP). The films were irradiated to a proton dose in the range of 0.5 Gy to 100 Gy. The beam profiles were also measured at the middle of the 24 mm SOBP. The Bragg peak was measured by using a wedge shaped phantom made of Lucite. The Bragg peak measured with RC film was compared with diode and ionization chamber measurements. After background subtraction, the calibration of the dose response of RC film showed, to a maximum deviation of 10%, a linear increase of optical density (OD) with dose from 0.5 to 100 Gy. The uniformity of OD over a single sheet of film showed a variation of ±6%. The distal-fall off between 90% and 20% measured with GafChromic film for the Bragg peak was 1.3 mm as compared to 1.1 mm for a diode measurement and 1.4 mm for an ionization chamber measurement. The FWHM of the Bragg peak was 7.5 mm when measured with GafChromic film, 5.3 mm when measured with a diode and 8.1 mm as measured by an ionization chamber. The peak/plateau ratio with GafChromic film was 3.3 as compared to 3.7 with a diode and 3.2 with an ionization chamber. In conclusion, GafChromic MD-55 film may be a useful and convenient detector for dose measurement and quality assurance programmes of proton beams.

A novel 675.2 nm diode laser densitometer for use with GafChromic films

In this article we compare the accuracy of a diode laser densitometer emitting 675.2 nm to that of a commercial He-Ne laser densitometer emitting 632.8 nm for GafChromic MD-55 film readout. A Leksell gamma unit (AB Elekta Stockholm, Sweden) Model B with a 14 and 8 mm collimator at the same isocenter (combined 11 mm collimator) was used to irradiate GafChromic MD-55 films. Dose response curves, dose cross profile and FWHM were measured with a custom-designed diode laser scanning device, emitting light at 675.2 nm. The same data were recorded with a commercial He-Ne laser densitometer (PTW FIPS Plus, Freiburg, Germany), emitting light at 632.8 nm. Both measurements were compared to dose cross profiles of a radiosurgery dose planning program (GammaPlan 5.12, Elekta, Sweden). Compared to the commercial He-Ne laser densitometer, the custom-designed diode laser scanning device showed better agreement with the calculated dose cross profile. For two axes, the full width half maxima (FWHM) of the diode laser scanning device was within 0.1 mm deviation compared to the data calculated by the dose planning program. The FWHM of the commercial He-Ne laser densitometer was less accurate (1.6 and 2.1 mm deviation). Our data show that a diode laser scanning device using a light source emitting 675.2 nm increases the accuracy of a GafChromic MD-55 film readout. This greater accuracy may be related to the diode laser measuring the optical density close to maximum absorption of the GafChromic film MD-55 (671-675 nm).

Comparison of Readout Between a New Diode Laser Scanner and a Helium-Neon Laser Densitometer for GafChromic MD-55 Films

GafChromic MD-55 films were irradiated by the Vienna γ-knife unit with a 14 and 8 mm collimator helmet (spherical field of close to 11 mm diameter) at the same isocenter to compare the dose cross-profiles along the x and z directions with different scanning systems. Dose-response curves for GafChromic MD-55 film (Nuclear Associates Model No. 37-041) were measured using two different densitometer systems: a commercial He-Ne laser densitometer (PTW FIPS Plus, Freiburg, Germany) and a newly developed analog diode laser densitometer. For this purpose, we chose the diode laser as the light source, emitting at 675.2 nm with a single-mode surface, measured with a Lock-In Amplifier by a solar cell. The highest uniformity was seen in the change of absorption ranging from 4% to 6%, depending on the polarizing direction of the light with the new scanning system. The reproducibility of the reading method increases from 0.14% in the region of 2 Gy to 0.18% near 16 Gy. Measurements of the dose cross-profiles of the 11 mm collimator with the 675.2 nm laser scanner generally show good agreement with the values of the dose planning program. Reference studies with the He-Ne laser reveal a general tendency between 1.5 and 2.2 mm in diameter as compared to computer-simulated dose profiles and the 675.2 nm laser densitometer values.

Localization and System Integration Tests as Quality Assurance for the Leksell γ-Unit

Quality control in stereotactic radiotherapy of brain lesions with the Leksell γ-unit or the LINAC-facility is a must, as missing the target is the most serious error that can occur in that kind of treatment. We developed a quality assurance program to reduce this risk. To evaluate the accuracy of the procedure, which defines the target, including all possible errors of the therapy chain, irradiations of phantoms were performed, using the so-called “known” and “unknown” target method. Accuracy is defined by the deviation of the irradiated target from the calculated target with digital images used for therapy planning. GafChromic MD-55 films, which have been irradiated by means of a special author-developed phantom, were applied for measuring the precision of the radiation unit. The results obtained for isocentric accuracy of the Leksell γ-unit were in good agreement with the measurements of the manufacturing company. The deviation measured with the 4-mm collimator helmet was up to 0.3 mm, including the CT images and the stereotactic frame less than 0.85 mm, respectively. The phantom designed for this purpose is useful in quality assurance measurements of this stereotactic therapy chain.